"Plastic pipe" is made from materials in the polyolefin family and its alloys, primarily because polyolefin can be fused together rather than glued or joined with rubber gaskets. Polyolefin pipe is replacing ball and spigot PVC pipe, ductile iron pipe, vitrified clay pipe, concrete and even steel pipe, where heat, high pressure, and deflection from ground loading are not factors of concern. Polyolefin pipes are almost completely unaffected by corrosive and unstable ground conditions. For example, polyolefin pipe is being used to transport corrosive chemicals, waste water, potable water, storm water, and for irrigation systems, leachate systems, and petrochemical collection systems.
A number of circumstances require fusing two pieces of polyolefin pipe together. The process of fusing polyolefin pipe consists of placing two matching surfaces on either side of a heat source, heating the surfaces to a predetermined temperature, removing the heat source, and forcing the two surfaces together under pressure.
Various factors affect the fusing of two pieces of polyolefin pipe. Polyolefin pipe is manufactured in many different wall thicknesses and diameters. In addition, fuses of the two pipes may be performed in a wide range of environments, from shops with controlled conditions to open pits subject to ground and weather conditions. An effective fusing apparatus would have to adapt to all such conditions. Further, depending on the result desired, the two pieces of pipe may be fused end to end (butt fusing) or with the end of one joined to the sidewall of the host pipe (sidewall fusing). Butt fusing is generally easier to accomplish. Sidewall fusing is accomplished by either of two methods: (1) fusing a fabricated saddle with a pipe nipple already attached onto the sidewall of the host pipe; or (2) fusing a sidewall pipe onto the host pipe. In order to perform a successful fuse in the latter case, the concave radius of one end of the sidewall pipe must match the outside convex radius of the host pipe.
Prior art devices accomplishing sidewall fusing are described in U.S. Pat. Nos. 3,998,682, 4,533,424, 4,542,892, and 5,613,807. Fusing machines currently being used employ manually-operated screws, hand-pumped hydraulics, auxiliary-powered, high pressure hydraulics, or a combination of these in order to provide the movements and pressures necessary to complete a sidewall fusion. Machines employing manually operated screws or hand-pumped hydraulics are slow, preventing an operator from joining the heated surfaces together quickly after the heat source is removed. Auxiliary-powered, high-pressure hydraulic machines must have valves, hoses, and cylinders capable of operating at high pressures, making the machines heavy and expensive; additionally, replacement power units for such machines are not readily available at rental outlets and contractor supply houses.
U.S. Pat. Nos. 5,364,207, 5,339,335 and 5,613,807 disclose and claim methods and apparatus for fusing a pipe onto the sidewall of a host pipe. The patents disclose fusing when a sidewall pipe is situated perpendicular to the axial alignment of the host pipe. None of the patents disclose a method or apparatus for performing a fuse when the sidewall pipe is situated at an angle other than 90.degree. to the axial alignment of the host pipe.
A number of circumstances require the fusing of sidewall pipe to a host pipe at an angle that is less than 90.degree.. Due to flow characteristics (i.e., sewer service leads), designers may need to have the flow enter a pipe in the direction of the existing flow. Presently, the only ways to accomplish this are: (1) cutting into the previously sealed line and inserting a fitting, using a wrap-around clamp to seal the cut; (2) fusing a sidewall pipe at a 90.degree. angle and using prefabricated bends to obtain a different angle; or (3) purchasing a fuse-on saddle with a fabricated nipple already attached at the desired angle. The latter fitting costs over twenty times the cost of a 90.degree. sidewall fuse. In addition, the saddle fitting only has a short nipple, and an adapter fitting or coupling is needed to extend the sidewall saddle nipple.
An apparatus which accomplishes fusing at an angle of less than 90.degree. would be a far less expensive method of providing an ideal, sealed system. However, such an apparatus would have to solve the problem presented by applying fusing pressure to an angled sidewall pipe when it is being fused onto the host pipe. Ordinarily, when pressure is applied to a sidewall pipe in any configuration other than perpendicular to the host pipe, the heated surface of the sidewall pipe in contact with the heating plate or the heated portion of the host pipe will begin to migrate (slide), along a path in axial alignment and radial perpendicular alignment with the host pipe, in the direction of the angle supplementary to the angle formed by the alignment of the sidewall pipe to the host pipe. In addition, such an apparatus would have to be able to be easily removed after an angle fusing operation is completed. None of the apparatus and methods disclosed in the prior art are capable of performing such angled fuses.